1. Field of the Invention
The present disclosure generally relates to a developing agent regulating member, a development unit and an image forming apparatus employing a developing agent regulating member, and a method of manufacturing a developing agent regulating member.
2. Description of the Background Art
In general, an image forming apparatus employing electrophotography includes a development unit for developing a latent image as a visible image, such as, for example, a toner image. The development unit includes a developing agent carrying member having a magnetic field generator such as, for example, a magnet provided therein, and a developing agent regulating member. The developing agent carrying member carries a given amount of developing agent on its surface using magnetic force of magnetic field, and the developing agent regulating member regulates a layer thickness of developing agent (hereinafter, agent layer) on the developing agent carrying member before the developing agent is transported to a developing area. Hereinafter, the developing agent regulating member may be referred to as a regulating member, and the developing agent carrying member may be referred to as an agent carrying member for the simplicity of expression.
Recently, an amount of developing agent transported to the developing area has been set to a smaller amount. Thus, an agent layer on the agent carrying member is set to be thinner by a regulating member.
The regulating member and the agent carrying member set a gap (hereinafter, doctor gap) therebetween. Specifically, one end face of the regulating member faces a surface of the agent carrying member across the doctor gap. Such an end face of the regulating member is referred as a regulating face of the regulating member. To set a thinner agent layer on the agent carrying member, the doctor gap may be set to smaller. However, it may be difficult to set a small doctor gap with higher precision.
In light of such difficultness of providing a small doctor gap, some related art propose a development unit that uses a regulating member that includes an attached magnetic member to set a relatively greater doctor gap while reducing a thickness of agent layer.
A doctor gap can be set greater by providing a magnetic member in a regulating member as described below. When a regulating member includes a magnetic member, a density of developing agent in the doctor gap can be set to a smaller amount as compared to a regulating member having no magnetic member.
When the regulating member includes the magnetic member, the magnetic member and a magnetic field generator (e.g., a magnet) disposed in the agent carrying member can form a magnetic field in and around the doctor gap, and chains of developing agent (hereinafter, agent chains) are formed along magnetic force lines. Such agent chains are formed with some interval spaces among adjacent agent chains, and thereby a density of developing agent in the doctor gap can be set to a smaller amount as compared to a regulating member having no magnetic member, in which chains of developing agent may not be formed between the regulating member and the agent carrying member.
If a density of developing agent in the doctor gap can be set small by forming such agent chains, an amount of developing agent passing the doctor gap may not fluctuate so much even if a distance of the doctor gap is changed (i.e., increased or decreased). Accordingly, a relatively greater doctor gap can be set while reducing a thickness of agent layer.
Such a regulating member is mainly composed of a magnetic member and a non-magnetic member. Specifically, the magnetic member is fixed on the non-magnetic member while setting one end face of the magnetic member and one end face of the non-magnetic member in a substantially flush state each other. The flush state face is used as a regulating face of the regulating member in which the regulating face faces the agent carrying member. However, the end face of the non-magnetic member and the end face of the magnetic member have some bump or step therebetween although both faces may be set in a substantially flush state.
If such regulating member including a bump or a step on the regulating face is used, an amount of developing agent passing the doctor gap may fluctuate over time. Thus, developing agent may not be supplied to a developing area as reliably.
Such fluctuation may occur as described below. When developing agent passes the doctor gap, toner may be softened by heat, such as frictional heat and heat transmitted from a heat source disposed in an image forming apparatus, for example. If the regulating member has a regulating face including a bump or step, such softened toner may enter, stick, and gradually accumulate in the bump or step. Further, other foreign materials may also enter, and stick to the bump or step. If such foreign materials cover the magnetic member, the intensity of magnetic force in the doctor gap becomes weak, and thereby agent chains may not be formed sufficiently in the doctor gap. If the agent chains are not formed sufficiently, a density of developing agent passing the doctor gap may become high, and thereby an amount of developing agent passing the doctor gap may increase over time. Accordingly, an amount of developing agent passing the doctor gap may fluctuate over time, by which developing agent may not be supplied to a developing area reliably.
Further, if the regulating face of the regulating member includes bump or step, foreign materials may locally accumulate in a direction perpendicular to a surface-moving direction of the agent carrying member. If foreign materials accumulate as such, an amount of developing agent passing a portion corresponding to accumulated foreign materials may become smaller, by which abnormal image, such as white streak may occur, for example.
Japanese Patent Application Publication No. 2004-191529 discloses a technology of using a clad plate as a regulating member. Specifically, a magnetic plate and a non-magnetic plate are stacked on one another, and bonded together by a rolling process to form a clad plate. Such a clad plate is cut, and a cut face of the clad plate is used as a regulating face of a regulating member. In such a regulating member, an end face of the magnetic plate and an end face of the non-magnetic plate may be set in a flush state with little bump or step.
However, such manufacturing method may have some drawbacks for manufacturing a regulating member having a relatively greater size, which is widely used in the market. If a regulating member having a great size is to be prepared by such rolling process, a great-sized rolling machine may be required, and thereby a manufacturing cost of regulating member may become high. Further, the clad plate having the magnetic plate and the non-magnetic plate may need to be fixed with a greater force using a specific device to prevent peeling of the magnetic plate and the non-magnetic plate when cutting the clad plate. Accordingly, such a configuration may increase a manufacturing cost of regulating member high.